Many electrical devices may be more conveniently used if they can be remotely controlled. For example, in an industrial application, such devices are mostly HVAC and lighting loads. The HVAC and lighting loads may be remotely controlled for a number of different reasons. For energy conservation reasons, some lights may be controlled by a timer. In other cases, different lighting intensity and different lighting distribution patterns may be desirable in a single building zone, depending upon its use. Each application suggests a different lighting level and different lighting distribution and they can vary over time, such as the change of seasons and changes in daylight in a given location. Normally, changes in the control of lighting levels, and distribution and timing of lighting zones is not done, or done very infrequently because it is inconvenient or impossible to do so with conventional controls. In retrofit applications the wiring often does not allow for controlling separate zones and/or lighting levels and the cost of rewiring is often prohibitive. Therefore, it is desirable to have a convenient, reliable way to remotely control individual loads or groups of loads in commercial/industrial lighting systems without having to rewire the loads in order to produce optimum control of different groups or patterns.
In addition to lighting systems, other devices can be conveniently remotely controlled. For example, powered gates and doors can be remotely controlled. Powered window coverings may be opened and closed, depending upon available day lighting. Fans, air conditioners or evaporative coolers can be activated or controlled depending on need, instead of by the circuit to which they are connected.
As electronic technology has advanced, a variety of control systems and communication methods capable of controlling lighting and other electric loads have become known. In order to be useful as an industrial lighting control system, certain requirements of the communication system and method are important. A system must permit both small and large groups of lights to be controlled on command. One problem relates to the connection and communication between the controller and the lighting loads. For example, almost all conventional connections that can control individual fixtures or complex groups or zones of lights are hard-wired. These systems rely on some type of control wires or optical cables being run to all the fixtures being controlled. The cost of installing additional wiring to retrofit existing buildings is prohibitively expensive. Usually the cost of this type of retrofit is more than the cost of the energy to be saved, which make such a project not practical. Another disadvantage of any hard-wired system is that it may be very costly to change the configuration if the use pattern changes. For example, a manufacturing plant may change the configuration of its production zone layout every few years. Depending on how the different lighting zones are initially wired it may be impossible to match the old or original lighting zones to correspond to new or desired manufacturing and lighting zones, thereby requiring all lights to be left on 24 hours a day, for example, and thereby using energy unnecessarily. Also, while conventional, radio frequency type connection systems are known, they have proven to be difficult to implement because of FCC low signal strength level requirements. RF systems in general, and especially systems using low signal strength levels, are subject to numerous reliability problems associated with interference and attenuation. Interference and attenuation problems are much more severe in the commercial and industrial environments than in residential environments. In the United States many commercial and industrial buildings are constructed with large amounts of concrete, rebar and other metal. These materials cause significant reflection and attenuation problems for wireless communication methods. Also, the transmission and receiving circuitry for this type of control system is complex and relatively expensive. At present, there is no known widely deployed wireless industrial lighting control system.
In an electrical distribution system, both the controlling device and interface device, such as a repeating device, as well as the loads to be controlled can be connected to the same circuit(s). It therefore would be useful to use the powerline circuits as the communication-connecting channel or means. Known, prior powerline communication systems have had difficulties employing the powerline as a communication channel because, once attenuated by the powerline circuitry, the communication signals are relatively small compared to the background noise. This is particularly significant in the commercial/industrial three-phase environment. As is well known, between certain locations in an industrial electrical system application there will be very high attenuation of any transmitted signal(s). As is also well known, it has been difficult to reliably separate the highly attenuated communication signals from the background noise on the powerline, particularly in such locations. A variety of modern, energy efficient devices, such as florescent ballasts and variable-speed motor drives, cause relatively large amounts of both radio-frequency (RF) and powerline noise. This makes matters worse in a typical industrial application, such as parking structure or warehouse because there are usually very numerous loads to be controlled, and at relatively long distances. All these contribute to very difficult situation, and harsh environments for any retro-fitable RF or powerline technology. These are the primary reasons there has been no technology that has successfully addressed these problematic situations.
The above-describe attenuation problem is further aggravated and complicated by the constant and unpredictable nature of changes in the noise and signal attenuation characteristics in the powerline. These changes result as various loads are connected and disconnected both on the circuits connected to a circuit breaker panel to which the loads are connected and on the circuits connected to any of the, typically, many neighboring circuit breaker panels attached to the same mains power transformer. Since the widespread introduction of variable speed drives used for HVAC applications and the widespread introduction of many different types of electronic ballasts for lighting use, these noise and attenuation problems have become much worse due. These drives and ballasts are significant noise generators, particularly in the commercial/industrial environment. Finally, communication of control signals through the powerline circuit in an industrial application is further complicated and hindered because the powerline in an industrial building includes and is affected by all of the circuit breaker panels and all the loads attached to the mains power transformer. No known, practical way is available to avoid these complications.